1. Field of the Invention
The present invention relates to a panoramic imaging device.
2. Description of the Related Art
Various devices for capturing images positioned therearound in a wide capture angle or range are known, such as a monitor camera and a monitoring system for monitoring obstacles around a car. For example, a known camera device for monitoring three directions around a car, that are front, left and right, uses prisms placed on the light entrance side of an imaging element, such that the prisms refract or bend lights entering in the left and right directions or ranges so as to form images in predetermined areas on the imaging element, while forming an image in a separate area on the imaging element based on light entering in the front direction or range without passing through the prisms. The formed left and right images and the formed front image are separately displayed on a monitor screen (refer, for example, to Japanese Laid-open Patent Publication 2003-207836). A known wide-angle imaging device uses multiple optical imaging units for forming optical images on an image plane or focal plane, such that the optical axes of the multiple optical imaging units intersect at one point near a lens, and that the image viewing angles or ranges of adjacent ones of the optical imaging units are contiguous. The images captured by the respective optical imaging units are reproduced as a panoramic image, which is displayed on a monitor screen (refer, for example, to Japanese Laid-open Patent Publication 2006-25340).
In the known imaging devices, there are problems to be solved. The camera device described in the first cited patent publication (Japanese Laid-open Patent Publication 2003-207836) makes it possible to obtain images in the three directions, front and left/right of the car. However, these images are displayed on the monitor screen as three independent images without being reproduced as a continuous image (panoramic image). Further, in order to allow the camera device to monitor a wide range such as about 180° (degrees) around the camera device, each of the three images in the three directions is required to have a picture angle of 60° (degrees) or larger. This requires the use of so-called wide-angle lenses as imaging lenses. However, a wide-angle lens is likely to cause barrel distortion at periphery of an image captured thereby. Although it is possible to digitally correct the barrel distortion at the peripheries of images, a complex program is necessary to correct the barrel distortion.
The wide-angle imaging device described in the second cited patent publication (Japanese Laid-open Patent Publication 2006-25340) makes it possible to reproduce a panoramic image from the images captured by the respective optical imaging units. When the wide-angle imaging device is used as a monitor camera, a high monitoring function can be obtained without causing so-called dead angles (non-imaging area) between the images. However, this wide-angle imaging device has a problem in that this imaging device is likely to become large in volume in its entirety because the multiple optical imaging units are placed three-dimensionally.